A projection exposure apparatus for EUV microlithography is known from U.S. Pat. No. 6,859,328 and from WO 2006/111319 A2.
In microlithography it is often desirable to illuminate a structure to be imaged with a predetermined polarization distribution because this can improve the contrast during imaging downstream of the structure. For this purpose, additional polarization elements have been used in the illumination optical unit, but the elements also absorb part of the radiation and thus can reduce the total transmission of the illumination optical unit.